In many cases it may be desirable when pumping fluid to avoid the fluid coming into contact with pumping components etc. This can avoid cross-contamination and keep the pumped fluid clean and sterile. This is particularly important in cases such as circulating blood for a patient undergoing surgery. A roller, or peristaltic, pump can be used in these circumstances.
FIG. 1 shows an example prior art roller pump 1 used to pump fluid, such as blood. The roller pump 1 utilises a flexible tube 2 in a circular portion of a housing 3 with a number of rotating rollers 4 housed on a rotor 5. These rollers 4 squeeze the fluid along the tube 2 in a continuous motion. The rollers 4 exert a force on the tube 2 which requires it to be firmly held at the entry 6A and exit 6B positions of the housing 3 to prevent the tube 2 “walking” through the roller pump 1 during continuous use. The restraining force that is required increases for higher pump speeds or pump pressures. The rotor 5 rotates clockwise, as viewed from above in FIG. 1, with the rollers 4 making contact and moving around the tube 2 accordingly. The tube 2 is constricted between the rollers 4 and the housing 3 as the rollers 4 rotate and this moves the fluid along the tube 2 in the direction of the arrows as indicated.
The outer diameter of the tube may be chosen depending on the current setup of the pump and the fluid it is pumping. A particular pump can take several different sizes of tube. Some existing pumps use features, e.g. grippers 7, which deform the tube in order to grip it—see FIG. 2. Others make use of removable inserts 8, 9, to enable different sizes of tube to be gripped—see FIGS. 3 and 4. Both of these methods are undesirable for different reasons, one puts a strain on the tube and also restricts the fluid flow within the tube. The other requires a library of parts to be able to fit different tube sizes, and the inserts 8, 9, must be removed and refitted.
The present invention has therefore been devised with the foregoing in mind. The invention seeks to overcome or ameliorate at least one of the disadvantages of the prior art, or provide a useful alternative.